Ieaskul F. Mobenthey IGM Keyboard


Interrogajoke: Grassi Mocante

Includes Mr. Grassi and Mocante in a wooden skiff.

Out of stock


The IGM keyboard (Interrogajoke: Grassi Mocante) is a completely alternative keyboard- a pitchwheel (Grassi) and a rack of keys (Mocante).


The Mocante module is a crossover from the Tocante series of touch-instruments, geared for Eurorack by Mobenthey. It features a twenty-four operator array of oscillators- in this case phase analysis units- tuned by capacitor series in the Tocante scale. As a touch controller, it outputs a control voltage representing the unique tunings of this scale, a gate signal, as well as a host of witches-tones and square-drones that derive from the Phase Lock Loop (PLL) machineries within.

Mocante is the first of Mobenthey’s ultra-raftable modules series, featuring all circuitry and the front panel on one circuit board. The final module thickness is only as deep as the 3.5mm jacks and potentiometers- not more than about a centimeter, so it can fit in a thin wooden case similar to those used for the Tocante instruments.

Mocante is a 54HP Eurorack module that runs on +12 and -12 volts. Actually it completely shuns the negative twelve volts, and thus it can run from a unipolar, plus twelve supply. This helps make it raftable, as it only requires a branch power line from the increasingly common 12V trunk. Thus, when ordered with a wooden case, it has a 2.1mm, tip positive, 12 V jack to power it. Also, it can be powered by 9 volt battery. If ordered without a case, for Eurorack mounting, it will come with a power connector traditional to that format.

Mocante has three main areas of touch:

  • Triangle Touch is the traditional touch controller, associated with the CV and Gate outputs. When untouched, the CV outputs an undefined voltage, and Gate outputs a logic low (about 0.4 volts). When touched, the CV outputs a voltage proportional to the frequency of the operator, and Gate goes high (between 4 and 7 volts).
  • Squares Touch takes the ultrasound machinery of each operator and octave shifts it into audible and subaudible ranges. When touched, they manifest an output at “Square Drones.” That jack is unbuffered so it can potentially act as input, to insert a signal into the toucher traces.
  • Circular Touch is the most ephemeral, associated with the hard and soft witches-tones outputs. It enables the ultrasound signals at each operator to heterodyne with others, creating audible whistling sounds and other noises… Soft witches-tones use heterodyne phase comparison to generate sweeter, sine-like sounds, whereas hard witches-tones use phase-lock pulses to make sawtooth forms.

Mr. Grassi

Mr. Grassi, a touch-module, contains twelve square waves, used as the clock and data for shift registers, each followed by primitive resistor DAC. The DACs modulate clock and counter-clock wise, yielding closed loops of perpetual modulation, triggered by touch. Each of the six outputs are a single, four-bit DAC. Listening to them raw, they generate modem sounds to pure noise on touch. On release of touch, each DAC holds the contingent position of its DATA. Thus the DATA can be used as CV for up to six other operators, scrambled on touch.

Touch->Scramble->Listen; Untouch->Hold->Feed.

Mr. Grassi, an ultra-raftable module, features all circuitry and the front panel on one circuit board. The final module thickness is only as deep as the 3.5mm jacks- not more than about a centimeter, so it can fit in a thin wooden case.

Mr. Grassi features a triangular hexagon, used for square-wave outputs (outer rim) and DAC triggers (inner core). Thus, a triggering touch should connect an outer station to an inner station, to begin the rungling process. Rungling, a coin of Rob Hordijk, is exactly what Mister Grassi does. He takes two oscillators and mixes them in the shift register chip, treating one as data and the other as clock. The result, a memory heterodyne, feeds back into the oscillators. This circular process traverses both analog and digital, soft tones and square drones.

Interrogajoke Manifesto
In order to propel the new ultra-raftable line of Mobenthey modules, a focus has been identified: that of the touch controller. An insider of the synthesizer clearing house has made this clear. The interrogajoke concept was formed to interrogate and also play about the touch interface. Is it a piano? How does it feel the finger? How does the finger feel it?

The most compelling question is the middle one; most touch devices use a high frequency signal that courses through the fingers and senses their capacitance. Although this is a signal, the module neglects it as unseemly ultrasound and denies it sonic presence. That is the core of the interrogajoke- how to give sonic presence to capacitive sensing waves. The toucher is a body without organs- it is not filled with knobs and switches that demand legends, but rather the cryptic runes inspired by sensor fields. As such, it is a place for bumbling fingers, not the precise en-goaled tweaker.

Additional information

Weight 0.275 kg
Dimensions 13 × 7 × 18 cm